1. Field of the Invention
The present invention relates in general to an AC drive discharge type display apparatus and more particularly to an AC drive discharge type display apparatus having a drive circuit for applying a sustaining drive voltage, a turn-on pulse and a turn-off pulse to a matrix type display panel.
2. Description of the Prior Art
FIGS. 1a and 1b are respectively a partially broken schematic view of one embodiment of a display panel used for a conventional AC drive discharge type display apparatus, wherein the reference 1 designates a glass plate; 2 designates linear electrodes; 3 designates an insulation layer, 4 designates a discharge gap; and 5 designates a spacer.
In the display panel, the two sheets of glass plates 1 having the plurality of linear electrodes 2 on which the insulation layer 3 is placed, are formed with the discharge gap of fixed length by the spacer 5 so as to cross the linear electrodes 2 of each sheet.
The cross points of the linear electrodes 2 of the display panel are respectively luminescent dots which can be separately turned-on or turned-off. The luminescent dots provide the picture elements for display.
In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. FIGS. 2a-2c are diagrams of waveforms for illustrating the various states of voltage application during the time of driving of the discharge panel, wherein the reference numeral 6 designates a sustaining drive voltage; 7 designates a turn-on pulse; 8 designates a luminescent pulse; and 9 designates a turn-off pulse. The operation of the display panel of FIGS. 1 a and 1b will be explained by referring to FIGS. 2a-2c.
In order to drive the display panel, the AC sustaining drive voltage 6 of FIG. 2 a is applied, in a normal state, across the discharge gap 4 through the two groups of the linear electrodes 2. The turn-on pulse 7 which has a level higher than the discharge initiation voltage V.sub.f is applied between the two linear electrodes 2 crossed at the turn-on point at the time of turn-on, whereby a discharge results only at the cross point. Once the discharge occurs, the luminescence is intermittently maintained until the turn-off pulse 9 of FIG. 2a is applied. Hereinafter, one group of the linear electrodes 2 in the two groups is referred to as X electrodes (X drive lines) and the other group is referred as Y electrodes (Y drive lines).
In order to apply the voltages of FIG. 2 a, i.e. the sustaining drive voltage 6, the turn-on pulse 7 and the turn-off pulse 9 across the discharge gap 4, the voltage of FIG. 2 b which is the sustaining drive voltage 6a, the turn-on pulse 7a and the turn-off pulse 9a is applied to the X electrodes and the voltage of FIG. 2c which is the sustaining drive voltage of FIG. 2c which is the sustaining drive voltage 6b, the turn-on pulse 7b and the turn-off pulse 9b is applied to the Y electrodes.
Incidentally, the turn-on pulses 7a and 7b respectively have a level of one-half of that of the turn-on pulse 7, and have reverse polarities to each other. The turn-off pulses 9a and 9b respectively have a level of one-half of that of the turn-off pulse 9 and have reverse polarities to each other.
FIG. 3 is a diagram illustrating one embodiment of the drive circuit for the display panel of the conventional AC drive discharge type display apparatus, wherein V.sub.s designates a sustaining drive voltage terminal; V.sub.p designates a turn-on voltage terminal; S.sub.ai (i = 1,2,3) S.sub.bj (j = 1,2,3 ) designate selective switch circuits; and E.sub.ij (i,j = 1,2,3) designate output terminals. The drive circuit is a matrix type circuit wherein AND circuits are formed by the resistances and the diodes.
In FIG. 3, nine lines of the linear electrodes 2 (FIGS. 1a and 1b) are given as the X electrodes of the display panel, and accordingly each linear electrode is connected through the respective output terminal E.sub.ij to three elements which consists of two diodes D.sub.a, D.sub.b and a resistance R.sub.a.
In the drive circuit, the sustaining drive voltage 6 having the waveform of FIG. 2b, is applied as an input to the sustaining drive voltage terminal V.sub.s, and is passed through the diode D.sub.a to the output terminal E.sub.ij for the X electrode at the charge up time and is then passed at the discharge time through the diode D.sub.b and a selective switch circuit S.sub.bj of a switch element, e.g. a transistor which is usually in the ON state, to the sustaining drive voltage terminal V.sub.s.
Incidentally, the selective switch circuit S.sub.ai is usually in the OFF state. In order to apply the turn-on pulse shown in FIG. 2b, one switch of the first selective switch circuit S.sub.ai which is connected to the turn-on voltage terminal V.sub.p, is turned on and one switch of the second selective switch circuit S.sub.bj is turned off, whereby the turn-on pulse 7a is applied through one terminal of the output terminal E.sub.ij to one linear electrode 2 of the X electrodes of the display panel. For example, when the turn-on pulse 7a is applied to the X electrodes which are connected to the output terminals E.sub.22, the switch S.sub.a2 is turned on and the switch S.sub.b2 is turned off, whereby the current is passed through the three transverse resistances R.sub.a which are connected to the switch S.sub.a2. However, since the switches S.sub.b1 are in the ON state, the current passing through the vertical lines is passed through the diodes D.sub.b and the switches S.sub.b1, S.sub.b3 to the sustaining drive voltage terminal V.sub.s. The voltage of the output terminals E.sub.21, E.sub.23 is kept at the same level as that of the terminal V.sub.s by the voltage drop in the resistance R.sub.a and accordingly the turn-on pulse 7a is not applied to the X electrodes which are connected to the output terminals E.sub.21, E.sub.23 and accordingly the turn-on pulse 7a is applied only to the X electrode which is connected to the output terminal E.sub.22 in the line of the switch S.sub.b2 which is in the OFF state. The selectivity is determined by the characteristic of the AND circuits which consist of the resistance and the diodes. The turn-off pulse 9a (FIG. 2b) can also be applied separately to each of the linear electrodes of the X electrodes in a manner similar to that of the turn-on pulse 7a.
Certain problems exist with the conventional drive circuit for the display panel using the AND circuit system of the resistance and the diode in that disadvantageously a large consumption of power is required, since unnecessary current is passed through the resistance R.sub.a to the circuit connected to the linear electrodes 2 to which the turn-on pulse and the turn-off pulse are not applied. Moreover, the conventional drive circuit also disadvantageously requires three circuit elements, namely two diodes D.sub.a, D.sub.b and one resistance R.sub.a, for each linear electrode 2, and accordingly the number of circuit elements is large.